Constant-speed electric motor



C. T. ALTFATHER CONSTANT SPEED ELECTRIC MOTOR Filed Sept. 27, 1947 2 2 fin w m. w 8 7 1 iv. 2 9 1 a 7 M8 I 2 m 3 i a 2 I w Z /7 %A// //%u a 4 w 2 FM. 2 L5 4 I Q IL. 2

INVENTOR 60/7 ru 0 r/4/iyh if. BY ATTORN Y June 21, 1949.

WITNESSES: 6/

Patented June 21, 1949 UNITED STATES PATENT OFFICE CONSTANT-SPEED ELECTRIC MOTOR Application September 27, 1947, Serial No. 776,543

8 Claims. 1

The present invention relates to electric motors and, more particularly, to a small, constant-speed motor which will operate at substantially the same speed on either alternating current or direct current.

Small, constant-speed electric motors, such as are used for timing purposes, have heretofore usually been alternating-current synchronous motors, which run at a fixed speed determined by the frequency of the current. There are numerous applications for these motors, however, where operation on direct current may be required, but no satisfactory type of motor has been available which could be used on either alternating current or direct current, and where direct-current operation has been required, it has been necessary either to utilize some different type of motor entirely, or to resort to the use of an inverter, or equivalent means, for operating an alternating-current motor from a directcurrent source. Either of these expedients is, of course, undesirable.

The principal object of the present invention is to provide a constant-speed electric motor, suitable for use as a timing motor, which is capable of satisfactory operation at substantially the same constant speed on either alternating current or direct current.

The motor of the present invention is of a type in which the rotor is rotated by magnetic attraction between salient poles on the rotor and a stationary driving electromagnet which is intermittently energized, the energization of the driving magnet being controlled by contacts which are actuated by a vibrating spring kept in vibration by magnetic attraction between the salient poles of the rotor and a permanent magnet on the spring. Such a motor will run at a constant speed determined by the natural frequency of vibration of the spring, but motors of this type have heretofore been capable of satisfactory operation only on direct current. It is an important object of the invention to provide a motor of this type which will operate satisfactorily, and at substantially the same speed, on either alternating current or direct current.

Another object of the invention is to provide an electric motor of the type described which will always be reliably self-starting regardless of the position in which the rotor may have stopped after a previous period of operation, that is, regardless of whether the contacts which control the energization of the driving magnet are open or closed.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a side View of the motor with one of the side-plates omitted;

Fig. 2 is a transverse sectional View, approximately on the line IIII of Fig. 1;

Fig. 3 is a fragmentary side view similar to Fig. 1, but showing the rotor in a different position;

Fig. 4 is a sectional view, approximately on the line IV-IV of Fig. 3; and

Fig. 5 is a schematic diagram showing the electrical connections of the motor.

The motor shown in the drawing is supported between two metal side-plates l, which are fastened together, and spaced apart, by bolts 2, or in any other suitable manner. The motor has a rotor member 3, mounted on a shaft 4 which is supported in bearings 5 of any suitable type secured in the side-plates I. The rotor 3is made of a suitable magnetic material, such as soft iron, and is generally disc-shaped with a plurality of salient pole portions. Four poles 6, 1, 8 and 9 are provided in the particular embodiment illustrated in the drawing, and each of the salient pole portions extends radially from the body of the rotor 3 and is bent axially at its outer extremity, as clearly shown in Fig. 2. A flywheel I0 is preferably also mounted on the shaft 4 in order to somewhat increase the inertia of the rotating element so as to improve the operation on alternating current, as will be more fully explained hereinafter.

A main driving electromagnet H is supported between the side-plates I in any suitable manner. The driving magnet l I has a generally U-shaped, laminated core [2 of magnetizable material, and the arms of the core, which form the poles l3 and M of the magnet, extend into close proximity to the outer periphery of the salient poles of the rotor 3, and are arcuately shaped at their ends, as shown in Fig. 1. The core 12 is magnetized by means of a coil which is preferably divided into two coil sections l5 and I6 placed on the poles l3 and M, respectively. The poles I3 and M are spaced apart a distance approximately equal to the spacing between the rotor poles, and it will be apparent that if the coil sections 15 and I6 are energized when the rotor is in the position shown in Fig. 1, the rotor poles I and 8 will be attracted toward the magnet poles I3 and I4, respectively, and the rotor 3 will be given a rotational impulse in the counterclockwise direction.

The coil sections |5 and I6 are intermittently energized in order to give the rotor successive rotational impulses, and energization of the coil is controlled by means of a vibrating spring member 11. The spring. l'l may be a generally rectangular piece of spring steel, or other suitable material, and, in the illustrated embodiment, the spring I7 is supported from the side-plates I by, means of bracket arms l8 which are secured to the side-plates. The upper end of thespring I1 is clamped between the bracket arms l8, andv is insulated from them by means of insulating spacers IS. A permanent magnet is secured to the lower end of the spring H, by welding or brazing.

The spring I1 is somewhat ofiset from the vertical plane of the rotor 3, with the permanent magnet 20 closely adjacent the outer .periphery oithe salient polesof the rotor. Thus, when the rotor is in the position shown vin'l ig. l, with a pole opposite the magnet, the spring [1 will be drawn toward the rotor, as shown in Fig. 2; by the magnetic attraction between the rotor pole and the magnet 20. When the rotor has moved to the position shown in Fig.3, with the magnet 20 in an intermediate position between two poles of the rotor, the magnetic attraction is suflicient- 1y reduced to permit the spring i1 to swing away from the .rotor. The spring I! is angularly spaced from the center of theipole l 3 of the driving magnet II a distancesomewhat less than the spacing between the centers of the rotor poles.

A movable contact 2|. is carried on the spring ll, preferably. on a tongue portion cut out of the springpso as to avoid undue interference with free vibration of the spring. A cooperating sta tionary contact 22 is adjustably supported on the side-plate l'by means. of a screw 24. The contacts 2| and 22 are connected in the circuit of the magnetizing coil sections l5 and I6, so as to control their energization, and it will be appar ent that, as .the' spring I1 vibrates toward and away from the rotor, the contacts 2| and 22 will close and open, intermittently energizing the coils l5 and l fito' g-ive successive impulses to the rotor, as more *fully 1 explained hereinafter.

A stationary permanent magnet 23 is preferably mounted ononeof-the-side-plates. I. The purpose of the magnet 23 is to provide a. positioning force toassi'stwin stopping the rotor 3 in the position ofFig. 1 when :the motor is deenergized, and: the magnet '23 .is placed so that it:is angularly spaced from the spring l1 bya distance substantially equalfltozthe angular-spacing betweenad'jacentwpoles.of the rotor-'3, so thatthe magnetic attraction between the magnet 23. and an. adjacent. rotor pole helps to stop the rotor in the. desired position,

It isdesirable for the'rotor to stop in the position. of'Fig. v1 when'thernotor is deenergized so that the contacts 2|-and 22 will be closed. In spite of: the presence of; the p rmanen m n t 23, however, the rotor will sometimes, stop in the dead-center; positionrof Fig. 3. with the. contacts open. An auxiliary. electromagnet 25 is provided in .order to; make the..motor self .-starting, whenthis occurs. Theelectromagnet 25 includesa core. 26 which is supportedin any suitabiemanner from one. of the side-plates b means of .a bracket. 21. 1A magnetizing coil.28.is wound on the.COIBU2=6,..3,I1d.;8, .p01e. piece 29 is secured to. the coreandextends. close. to. the, outer periphery of the rotor poles. The pole piece29 is tion of the motor.

. after.

The. electrical connections of the motor are .shownschematically in Fig. 5. The coil sections .l5 ,and- I6 are connected in series and to the stationary contact 22. The other end of the coil is connected to a relatively large resistor 30, theother end of which is connected, preferably through a line switch 3|, to one side of the supply line 32, which may be either a directcurrent line or a single-phase alternating-current line. The spring I! is connected directly to the-other side of the line-32, so that when the contacts-2| and-22 are closed, the coil sections l5 and I6 are connected across the line in series with the resistor 30. A small resistor 33 and capacitor 34are preferably connected across the contacts to prevent sparking as the contacts rapidlyopen and-close. The'coil'ZB of the auxiliary electromagnet 25 is connected in a shunt circuit across the main coil sections l5 and I5 and the contacts 2| and 22, and is designed to have much higher impedancethan' the main coil. The impedance of the coil 28 should be at least five times the combined impedance of the main magnetizing coil sections I5 and I3, and its impedance is preferably made much higher than this minimum value, since a sufficient rotational effect on the rotor can be obtained, even with a highimpedance coil,-and the high impedance reduces heating of the coil 28 during continuous opera- When the contacts 2| and 22 close, the coil'28' is shunted by the relatively low-impedance coil sectionsl5 and IS, and thus the coil- 28 is eiiectively energized only when the main coil is deenergized.

The operation of the motor is as follows. When the motor is deenergized with the rotor 3 in the position shown in' Figs; 1 and 2, it will be seen that the spring H is drawn toward the rotor by themagnetic attraction between the permanent magnet 20 and the pole 6 of the rotor 3, and that the contacts 2| and 22 are closed. If the line switch 3| is now closed, the coil sections 5 and I6 are energized and the poles and- 8 of the rotor are attracted toward the poles l3 and M of the driving magnet. so that the rotor starts to rotate in the counterclockwise direction.

As the rotor pole 6 moves away from the magnet 20, the-magnetic attractionbetween the rotor and the permanent magnet 20 diminishes, and the spring swings away from the rotor to, or past, the position shown in Fig. 4, which opens the con- .tacts 2| and 22 to deenergize the coil sections I5 and Hi. The inertia of the rotor is sufficient to cause it to coastpast this point, and the succeeding pole approaches the position previously occupied by the pole 6 as the spring I! vibrates back toward the 'rotor in accordance with its natural frequencyof vibration, the return movement of the-spring being aided by the magnetic attraction between the permanent magnet 20 and the approaching pole 'l. This recloses the contacts 2 Land 22 to againenergize the coil sections l5 and I6 as the rotor poles 8 and 9 approach the magnet poles l3 and I4, respectively, thus giving another impulse of rotation to the rotor. It will be apparent that the rotor will continue to rotate under the successive impulses given to it by the driving magnet II, the frequency of the impulses being determined by the natural frequency of vibration of the sprin H, which is kept in vibration by the magnetic attraction between the successive rotor poles and the permanent magnet 20. Thus, the motor will run at a constant speed determined by the natural frequency of the spring If the coil of the main driving magnet I I were connected directly across the line 32 without the resistor 30, the motor would run as described above on direct current. If it were attempted to operate the motor on alternating current, however, the operation would be unreliable and unsatisfactory because, if the contacts 2| and 22 should close at or near a zero point of the voltage wave, the contacts would reopen before any appreciable impulse would be given to the rotor, and the motor would slow down or possibly stop, depending on the inertia of the load. Since this might occur frequently, or even on successive closures of the contacts, the motor would not run at constant speed, or might not run at all, and operation on alternating current would be unreliable and unsatisfactory. For this reason, motors of this type have been suitable for use only on direct current.

If the coil sections l5 and |6 are designed for low voltage, however, and a relatively large resistor 3% is connected in series with them, as shown in Fig. 5, the time constant of the circuit is sufficiently reduced so that the current in the circuit, and the resultant magnetic flux, build up at a relatively rapid rate when the contacts 2| and 22 close, and even if the contacts close near a zero point of the voltage wave, sufiicient current will flow, and it will build up sufficiently fast in the coil, to give an appreciable driving impulse to the rotor to maintain uninterrupted and reliable rotation without appreciable change in speed. In order to obtain this effect, the resistance must be relatively large, and it has been found that satisfactory operation is obtained if the resistance of the resistor 3!! is such that the voltage across the main coil sections I5 and I6 is not more than about 26% of the line voltage applied to the motor.

Because of the rapid interruption of the current by the contacts 2| and 22, the voltage drop across the main coil is much greater than the resistance drop alone, even on direct current, and the resistance of the resistor must be determined in view of this effect. In one specific embodiment of the invention, good results have been obtained with a resistor 3|) having a resistance about fifteen times the combined direct current resistance of the coil sections l5 and IS.

The provision of the flywheel ID on the shaft 4 also improves the operation on alternating current, since it helps the rotor to coast through periods of weak driving impulse, resultin from the closure of the contacts at a low point on the voltage wave, without noticeable loss of speed. It is not necessary to greatly increase the inertia of the rotor, however, and a relatively small flywheel is to be preferred since, if the inertia of the rotating member is too high, it may cause slow or uncertain starting of the motor, and a longer period of coast after the motor is deenergized, which may be undesirable in some applications. It will be obvious, of course, that the rotor 3 might be designed with sufficient inertia to make it possible to omit the flywheel, but the use of a separate flywheel usually makes it possible to obtain the desired effect with less total weight.

The provision of the auxiliary electromagnet 25 is an important feature of the invention, since it insures reliable starting of the motor. It would be desirable for the rotor 3 to always stop in the position of Figs. 1 and 2 when the motor is deenergized, since the contacts 2| and 22 are closed in this position, and the motor will restart immediately upon closure of the line switch 3|. The permanent magnet 23 provides a positioning force which tends to stop the rotor in the desired position, but in spite of the presence of this magnet, the rotor will sometimes stop in the deadcenter position of Fig. 3 in which the permanent magnets 20 and 23 are midway between adjacent r-otor poles. Since the contacts 2| and 22 are open when the rotor is in this position, the motor would not then be self-starting. The auxiliary electromagnet 25 is provided to effect starting of the motor when the rotor is in the dead-center position and, as shown in Fig. 3, its pole piece 29 is positioned so that when the coil 28 is energized, the adjacent rotor pole will be attracted toward the pole piece 29 and the rotor will move counterclockwise.

The auxiliary magnet 25 does not have to be very strong, since only a relatively small force is required to move the rotor from the dead-center position, and as soon as it has so moved, the magnets 20 and 23 will attract the rotor to the position where the contacts 2| and 22 will close, and the motor will then continue to run as described above. The coil 28 of the auxiliary magnet 25 is a high-impedance coil, as previously described, and it is efiectively energized only when the contacts 2| and 22 are open, since the coil 28 is substantially short-circuited by the relatively lowimpedance coil sections IS and I6 when the contacts are closed. Thus, there is no tendency for the auxiliary electromagnet 25 to cause any negative torque when the motor is running, but

it insures positive and reliable starting of the motor irrespective of the position of the rotor.

'It should now be apparent that an electric motor has been provided which is reliably selfstarting and which is capable of constant-speed operation on either alternating current or direct current, the speed of the motor being determined by the natural frequency of vibration of the spring so that it is substantially independent of the frequency when used on alternating current. A preferred embodiment of the invention has been shown and described for the purpose of illustration, but it is to be understood that various other embodiments and modifications are possible within the scope of the invention. The invention is therefore not limited to the particular details of construction shown and described, but in its broadest aspects, it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

I claim as my invention:

1. An electric motor comprising a rotor member of magnetic material having a plurality of salient pole portions, a pole member of magnetizable material adjacent the rotor member, said pole member being positioned to attract said salient pole portions of the rotor member to effect rotation of the rotor member, a magnetizing coil on the pole member, a vibratory spring member mounted to vibrate axially of the rotor member, a permanent magnet supported on said spring member in position to be attracted by the salient :poleuportions of: the rotor memben; con. tact'means actuated-by movement of:the spring. member for controlling the. energization of. said magnetizing coi1,..and-:alfixed-resistor. connected iniseries. with :said coil; the resistance. ofisaidrrree 5 sister: being relatively large asrcomparedtoithats. of: the magnetizing coil; sothatthetimeconstant ofwthe; series circuita comprisingithe resistonanda: coir is substantially 'less than. that 50f :theacOil; alone.

2." An electric motor ascdefined .in.=:claim -.-1 inn which the resistance of the resistoraisrsuch.that; thwoltage across .the-coil isinot moreethanaboutx 'of the voltage appliedrto the series'circuit comprising the resistoraand-cOil; I 15,

3...An electric-motor comprising a rotor mem ber; ofLm-agnetic' material: having a plurality, oirm. sallentpole portions a .polemember of magnetizedabl'e'1-=material adjacent the .rotor .member-,.-said: pole-member being. positionedato: attract asaidnigg salient: pole portions of the rotor. member to: ef-z v Iect rotation ofthe rotor member, a magnetizing...- coilr-onxth'e polemember, a vibratoryspring mem.-. bermounted-to vibrateaxiallyof the rotor mema a ber;;: a permanent magnet supported: on said spring. member in 1 position toabe attracted by the l salientvpole portions 2 of. the rotor member, cone tact means actuated by movement of the springs member; said contact: means being 'connectedto control the; energization of' said-magnetizingcoilfi whereby-the coil: istinter-mittently energized-es:- the spring member .vibratestoward and away from: :the; rotor: :member w andauxiliary ele'ctro'--- magnetic means positioned-toattract the salient-I pqle portions ofthe rotor member to effect rota-- tion of the rotor member, said auxiliary -electr-o--:- magnetic meanssbeing connected to beuelfectively t energized :only. \when;saidmagnetizingcoil is de energized. 1

4.,'An11e1ectriC mDtO'I" Comprising a 'lot0rmemmean being onnected to ontrol. energizahereof magnetic material havinga plurality ofsalient polezportions, a pole memberofmagnetiz' able'material adjacent: the rotor member, said pole member-being positioned'to attract said salient pole portions of:the=rotor member-to effe'ct rotation of.- .the rotor member a magnetizing coil on the. .13010 member, a vibratory spring member mountedrto vibrate axially ofthe rotor memberv a permanent magnet supported-pn" said spring member in position to be attracted by the salient pole'iportions ofthe rotor member, contact means": actuated bymovement ofthe spring memberysaid contact means beingconnected'tocontrolthe; energizationci said magnetizing COlL'WhEI'GbY'thG" coil is intermittently energized-as the spring-mem v ber: vibrates towardand awayfrom; the -rotor;;-- member; and auxiliary electromagnetic means-p0 sitioned-toattractthesalient poleportions ofthe rotor member'to effect rotation of the rotor mem'-- berg saidauxiliary electromagnetic meanshaving 60,

a pole piece and a m'agnetizing'coil, and means for connecting said last-mentioned coil in ,shunt' "1. relation=to the first-mentioned coil and the com: tact means,-the coil of the,auxiliaryelectromage netic means having relatively high impedance as compared-to that ofthefirst-mentioned coil;

5. An electric motor as definedin claim 4 .in which the, impedance "of ,the magnetizing coil of, I the auxiliary electromagnetic means is. at least five times the impedance ,ofthe first-mentionedgflq coils,

6. An electric motorcomprisinga rotorimemr. ber of magnetic. material having, .a ,pluralityfoi salient pole portionaa pole memberormagnetize able; material adjacent thev rotor, member, said pole memben being positiOtlfid to;; attractsaid 1 salientpole pQrtions of therotormember-to. effect rotation of-the rotor member; a magnetizing coil ,1 ,on the pole member, a resistor connectedin series with .said 0011,; a ,-:vibratory; spring member. mounted to vibrate axially of the rotor=member,-

a permanent. magnet. SuppQrted-onsaid spring member in position to-be attractedbythe-salient. pole pol'tions'of the rotor member, contactmeans.

actuatedby movement of the spring; member, said contact means being connected to control the energization of said "magnetizing coil, whereby positioned .to attract the salient pole portions of thetrotorlmemben to effect rotation of the rotor member, said auxiliary electromagnetic-means being.connected :to be efiectively energized only;

when said magnetizing-coil is .deenergized.

7., An.electric motor-comprising airotor member of magnetic. m'aterialhaving aplurality of salient pole-portions, a pole member ofmagnetizgable. materialadjacent the rotor member, said pole member being positionedtoattractsaid salil entpole portions of the rotor member to effect rotation of the rotor member, a .magnetizing coil on the pole mem'ben-a resistorconnected in series. --with said coil, the resistance of said resistor being such that the time constant of theseries circuit. comprisingthe resistor andecoil ,is substantially less than the time constant of the coil alone, ,a vibratory spring membermounted to vi-.

ibrate axially of the .rotor member, a permanent magnet supl Orted on said-spring member in position, tobe attracted by the salient pole portions ofthe rotor member, contact means actuated by movement of the. spring member, said contact tionof saidmagnetizing coil, whereby the coil is intermittently energized as the spring memberv vibrates toward and away from the rotor mem bar, and auxiliary.electromagnetic means positioned to attract the salient pole portions of the rotormember to effect rotation ofthe rotor meme ber, said auxiliary electromagneticlmeans having a pole piece. anda magnetizing coil, and

means for connecting said last-mentionedcoil in shunt relation to the first-mentioned coil and the contact means, the ;coil0f the auxiliary electromagnetic means having relatively'high impedance as compared to that of the first-mentioned coil.

8. An electric motor as defined in claim '7 in: which-the resistance of'the resistor is such that the=voltage across-the first-mentioned coil is not more than about"20% 0i" the-voltage applied to the series circuit comprising theresistor and coil,

and in-which'the impedanceof the magnetizing I coil-ofthe auxiliary electromagnetic means is at least five times the impedance of the first-mentioned coil...

CONRAD T. ALTFATHER.

REFERENCES ."CITED' The :following: references are of record in the file: of I this patent:

UNITED STATES PATENTS 

